There’s a hunger in psychology for birth-order effects—prophecies about personality that originate in whether your siblings are older or younger than you. Alfred Adler, a student of Freud, pioneered the idea that firstborns seek out leadership roles, delight in rules and order, and value achievement; that lastborns tend to be charming, popular, and spoiled; that middle children—yawn, who cares?; and that onlies can be both mature and dependent.

But many of the studies trying to back up these truisms with evidence use shoddy methodology that either fails to control for family size, economic status, or parents’ educational attainment or extrapolates about dynamicswithin a family from comparisons between families (e.g., the Smiths’ eldest earns higher grades than the Jones’ youngest, so firstborn kids do better in school).

New research from scientists at the University of Essex, though, uses multilevel modeling techniques to overcome these hurdles, and the results suggest that birth-order effects are more than just a methodological illusion. At least when it comes to academic achievement, the mythical yeti of family psych has been bagged and examined—call your older sister!

Feifei Bu looked at more than 1,503 sibling clusters and 3,532 individuals taking part in the massive British Household Panel Survey, which has been parsing the isle’s domestic DNA since 1991, and its successor, the U.K. Household Longitudinal Study. She finds that firstborns are more likely to be the “ambitious” and “accomplished” ones in their families. Firstborn girls especially outdo their siblings in educational dreams and attainment—they are 13 percent likelier to aspire to graduate school than firstborn boys.

On the other hand, the researchers write, “We see no evidence that the sex of one’s siblings has any effect on educational aspiration or outcomes. Nor do we find a strong relationship between sibship size and either educational aspiration or attainment.” (So you can’t blame your grades on how many siblings you have or what gender they are.) What does seem meaningful is the time spacing between children: Eldest kids separated from their brothers and sisters by a significant age gap—four or more years—are likelier, at 13, to express an interest in higher education, and they go on to pursue more advanced degrees.

Past studies indicating that firstborns have higher IQs than their siblings have launched speculation about why this might be (as well as taunts that the dumb middles and lastborns are too thick-skulled to push out their own competing studies). Bu floats several of these older hypotheses in reference to her results.

Confluence theory states that “children’s intellectual development is moulded by the intellectual environment in the family, which is a function of the average of the intellectual levels of all members of the family.” So the brain climate is loftier for firstborns than for younger sisters and brothers—at least until those younger siblings are born, after which, shouldn’t they be better-positioned than their elders? (Confluence theory doesn’t make a ton of sense to me. Perhaps I have an older sibling I don’t know about.)

Other, more plausible explanations: While parents, newly stunned by the miracle of life, invest more resources in their first child, the wondrousness has worn off by kid No. 3, who must fend for herself intellectually. Or firstborns are less constrained in their achievements by the need to differentiate themselves from a sibling—they get “first pick” of an identity, so it’s more likely to fit. Or—finally, and most simply—stereotypes about eldest-child excellence coalesce into expectations, which toughen into realities.

I wish the paper had tried to account for the particular ambition of firstborn girls. (The Guardian has a pretty persuasive list of power-playing female eldests that includes Angela Merkel, Hillary Clinton, Sheryl Sandberg, J.K. Rowling, Oprah Winfrey, and Beyoncé.) The result does seem to bulwark the fact that women are pulling ahead of men in educational attainment more generally, and that gifted girls prove especially vulnerable to pressure from their folks. One factor Bu and her team may have overlooked as they teased apart the family structure’s role in scholastic glory? Pets. If I have accomplished anything in my career as a daughter, it has been in quixotic pursuit of being loved as much as the dog.